AJP - Regulatory, Integrative and Comparative Physiology, Vol 256, Issue 2 313-R322, Copyright © 1989 by American Physiological Society
Ca2+-stimulated ATPase activities in the gill of the eel: interactions of Mg2+ ions
R. Naon and N. Mayer-Gostan
Laboratoire Jean Maetz, Departement de Biologie du Commissariat a l'Energie Atomique, Villefranche-sur-Mer, France.
Enriched plasma membrane preparations of the branchial epithelium of
freshwater-adapted eels were used to study adenosine triphosphatase
(ATPase) activities insensitive to ouabain and responding to Ca2+ and Mg2+.
Ca2+ induced ATP hydrolysis; two kinetics were observed in the presence or
absence of chelators, one with a high-affinity site (0.3 microM) and one
with a lower affinity site (10-20 microM). The high-affinity Ca2+ site or
enzyme had a prerequisite for Mg2+ (endogenous Mg2+ being sufficient to
satisfy the Mg2+ need) but was inhibited by exogenous Mg2+ (Ki0.5 less than
10 microM Mg2+). The low-affinity site or enzyme appears to have kinetic
parameters comparable to those found for Mg2+-induced ATP hydrolysis. In
the absence of Ca2+ ligands and with no exogenous Mg2+, the two Ca2+ sites
or enzymes can be considered stimulated. The results are discussed in
relation to the branchial ion environment and transport ion capacities.
